I recognize what you are asking. You want as much travel as you can get. It's better to have too much travel than not enough. Don't shoot for a minimum available travel, shot for a maximum notch, and hope it is enough.
Theoretically, you should have the same travel from the axle tube to the frame as you have from the top of the pumpkin to the underside of the bed. BUT, you will want more travel on the sides for when you are cornering hard AND hit a bump. Cut as deep as you dare. I don't cut more than half, but others do.
Do some google-foo and see what pictures shake up. Mini-notch, pipe-notch, and c-notch are common terms for this.